I think planting trees is always good, whether you're trying to say it's to reduce co2 or for shade, etc. The problem is when it's not properly planned. For example the trees should be planted in areas where they are expected to not be disturbed for decades. No point in planting them near road that might be widened a few years later.

I also share Darker's apprehension about maintenance. It should be part of the planning otherwise it'll be like buying a kid a bunny for Easter - it'll be dead within a week.